The present invention relates to an electrical socket for use with an electrical plug. In particular it relates to an electrical socket comprising means for preventing incorrect insertion of a single plug pin of an electrical plug into the socket.
A plug for use with the socket typically comprises two (Live and Neutral) or three (Live, Neutral & Ground) plug pins. The plug may have different configurations depending on the standards used in each country for electricity supply outlets. For example, in continental Europe the use of Live (L) and Neutral (N) pins only is standard whilst in the United Kingdom three pins are used so as to include a Ground (G) pin otherwise known as an earth pin as well as the L and N pins.
The socket of the present invention may be embodied in a mains socket as found fixedly located in walls or may be embodied as part of an extension cable or as part of a travel adaptor or similar transportable device.
The plug pins are electrically connected to the socket by inserting the plug pins into receptacles formed in the socket. Each plug pin receptacle comprises an electrical contact which permits an electrical connection to be formed between the plug and the socket when the plug pin is inserted into the receptacle.
For safety, it is known in some sockets to provide a shutter that shuts off or covers the socket receptacles when there is no electrical plug being connected to the socket. This is provided to prevent potential electrocution by the insertion of foreign bodies into the receptacles and thereby making contact with, especially, the electrical contact of the Live plug pin receptacle.
An example is a United Kingdom three pin socket. When an electrical plug is inserted into this type of socket, a shutter in the receptacles is activated by the G pin of the electrical plug to move the shutter to expose the L and N receptacles. The G pin is longer than the L and N pins and thus comes into contact with the shutter before the L and N pins when the plug is being inserted into the socket. When the G pin is connected and the shutter is pushed to open, the L and N pins can then be connected to the corresponding receptacles. The shutter cannot be opened by inserting just the L and N pins. A disadvantage is that this type of safety mechanism cannot be used with sockets having only two pins as there is no G pin on the corresponding electric plug which can be used to trigger the shutter.
Sockets without such a shutter have a potential danger of single pin miss-insertion. FIG. 1 shows just the L pin of a three pin plug 101 being inserted to one of the receptacles 102 on prior art socket 103 which does not contain a safety shutter, leaving its N pin 104 and G pin 105 hanging outside the socket 106. The exposed N pin 104 may carry an electric current and cause safety issues if the plug 107 is connected to an electrical outlet in this condition.
As noted above, two-pin sockets cannot use a shutter that is triggered by a G pin. To avoid the danger of single pin insertion, German sockets (which are of the two-pin type) for Schuko plugs are made with receptacles on a surface which are recessed into the body of the socket. The recess is deep enough in relation to the length of the plug pins so that making electric connection is impossible if the plug and pins are not inserted into the socket with the pins and receptacles correctly aligned. This solution can work for mains electric sockets where the size, in particular the depth, of the socket is not of high importance.
Another way to avoid single pin insertion is to make the socket to have the distance between the receptacles and the edge of the socket larger than the distance between the pins of the plug. In this way the housing of the socket itself prevents only one pin being inserted into a receptacle. However, especially for travel adaptors there is a wish to minimise the size of the adaptor and this solution results in a large socket which is not suitable for travelling. Also, design of such a socket requires knowledge of the spacing of the pins on all plugs in different countries that might be used with the adaptor.
There is therefore a need for an electric socket which can operate safely so as to avoid single-pin insertion and be suitable for use with two and three pin designs of sockets and be suitable for use in mains sockets, extension cables and travel adaptors.